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Activity 002: UV Exposure and Cure Depth Experiment

Activity ID: U2M1-ACT-002 Duration: 35 minutes Objective: Students will investigate how UV exposure time affects cure depth and print quality by testing different exposure settings on resin samples. Group Size: 2-3 students per station Materials Cost: ~$3-5 (small amount of resin per group)

Overview

Students use the resin printer to create a controlled exposure test — printing the same calibration pattern at multiple exposure times on a single build plate. By measuring the resulting cure depth and evaluating detail quality, students develop an intuitive understanding of how exposure parameters affect print outcomes.

Materials & Equipment Needed

  • MSLA resin printer (one per 2-3 groups, instructor-supervised)
  • Standard photopolymer resin (405nm, any color)
  • Exposure test STL file (provided — contains 5 identical squares at different Z-heights)
  • Digital calipers (0.01mm resolution)
  • UV flashlight (405nm, for demonstration only — instructor use)
  • Nitrile gloves (2 pairs per student)
  • Safety glasses (UV-blocking)
  • Wash station with IPA (90%+)
  • Paper towels
  • Comparison worksheet

Instructions & Procedure

Phase 1: Test Design and Setup (10 min) 1. Put on nitrile gloves and safety glasses before any resin contact 2. The instructor will prepare the printer with the exposure test file, which prints 5 identical 15mm × 15mm × 2mm squares, each at a different bottom-layer exposure time: - Square A: 50% of recommended exposure (under-exposed) - Square B: 75% of recommended exposure - Square C: 100% of recommended exposure (manufacturer default) - Square D: 125% of recommended exposure - Square E: 200% of recommended exposure (over-exposed) 3. While the printer runs (approximately 10-15 minutes), discuss with your group: - Predict which square will have the best dimensional accuracy - Predict which square will fail to print or detach from the platform - Predict how over-exposure will affect fine detail features

Phase 2: Print Removal and Washing (5 min) 4. When the print completes, the instructor will remove the build platform 5. Wearing fresh nitrile gloves, carefully remove the test squares from the platform using the scraper 6. Place all 5 squares in the IPA wash bath for 3 minutes, agitating gently 7. Remove from IPA and blot dry with paper towels 8. Label each square A-E with a permanent marker on the back side 9. Do NOT UV-cure the squares yet — we want to examine the "green state" properties first

Phase 3: Measurement and Analysis (15 min) 10. Measure each square with calipers and record: - XY dimensions (should be 15.00mm × 15.00mm) - Z height/thickness (should be 2.00mm) 11. Calculate dimensional error for each square: - Under-exposed parts may be thinner (incomplete cure depth) - Over-exposed parts may be wider and thicker (light bleed causes extra curing) 12. Examine surface quality of each square: - Look at the bottom surface (FEP-facing side) for detail and texture - Look at side walls for layer line visibility - Check edges for sharpness vs. rounded/bloated appearance 13. Perform a gentle flex test on each square: - Under-exposed squares may be soft and pliable (incomplete polymerization) - Properly exposed squares should be firm with slight flex - Over-exposed squares should be rigid and may be brittle 14. Rate each square on a 1-5 scale for: dimensional accuracy, surface quality, and rigidity 15. Create a graph plotting exposure time (X-axis) vs. each property rating (Y-axis)

Phase 4: Post-Cure Comparison (5 min) 16. Place all 5 squares under the UV post-cure lamp for 5 minutes (equal treatment) 17. Re-measure XY and Z dimensions after post-curing 18. Note any changes — post-curing may cause slight shrinkage (0.1-0.3%) 19. Compare the under-exposed square before and after post-cure: did post-curing compensate for insufficient initial exposure?

Discussion Points

  • Why does over-exposure cause parts to be dimensionally larger than designed?
  • Why can't you simply use maximum exposure to ensure complete curing?
  • How does resin color (pigment concentration) affect the optimal exposure time?
  • If you switch from a clear resin to a black resin, would you expect to increase or decrease exposure time? Why?

Expected Outcomes

  • Square A (50%): likely under-cured, soft, possibly incomplete, dimensionally thin
  • Square B (75%): slightly under-cured but mostly formed, minor dimensional errors
  • Square C (100%): best overall quality, closest to designed dimensions
  • Square D (125%): slight over-cure, features slightly bloated (+0.05-0.15mm)
  • Square E (200%): visibly over-cured, features significantly bloated, rounded edges, loss of fine detail

Assessment Rubric

Criterion Excellent (5) Proficient (3) Needs Improvement (1)
Measurements All dimensions measured precisely for all 5 squares, error calculations correct Most measurements complete with minor calculation errors Missing measurements or significant errors
Predictions Predictions for under/over exposure were accurate and scientifically reasoned Some predictions correct Predictions inaccurate with no scientific basis
Analysis Graph Clear graph with labeled axes showing exposure vs. quality relationship Graph present but incomplete or poorly labeled No graph or incorrect data plotting
Conclusions Correctly identifies optimal exposure range and explains the physics behind over/under exposure Identifies optimal range but limited explanation Cannot identify optimal range

Safety Considerations

  • Nitrile gloves are MANDATORY when handling uncured resin or unwashed prints — resin is a skin sensitizer
  • UV-blocking safety glasses must be worn whenever the printer lid is open or when using the UV flashlight
  • IPA is flammable (flash point 12°C) — keep away from the printer's UV light source and any heat sources
  • Do not pour used IPA down the drain — it contains dissolved resin that must be UV-cured before disposal
  • Wash hands thoroughly after removing gloves, even if no contact with resin occurred

Last Updated: 2026-03-19